The verbosity and output file options can be obtained from options
returned by `.parse_preliminary_options_and_args()`, instead of state
from the `Application` object.
This is the initial step towards removing state from the `Application`
object during argument parsing and handling. The goal is to remove
`Application.prelim_opts` and `Application.prelim_args`.
When calling `ArgumentParser.parse_args()` with the `namespace`
argument, command-line options are just added to the namespace without
going through any of the argument parsing and type conversion logic
(e.g., the `type` keyword argument of `ArgumentParser.add_argument()`).
In other words, it is assumed that a namespace is well-formed from a
previous invocation of `ArgumentParser.parse_args()`.
The `values` parameter is intended to be values already-provided from
configuration files. To take advantage of the logic defined by
`ArgumentParser.add_argument()`, utilize
`ArgumentParser.set_defaults()` instead.
Now that callers are ensuring that `value` is not `None`, we can further
tighten the contract and remove the conditional to account when `None`
is passed-in for `value`.
Additionally, add a new test vector to account for when an empty string
is passed in, which would fail `if no value`.
The `normalize_paths()` utility was doing too much — parsing
unstructured configuration path data and dispatching the scrubbed paths
to be normalized.
Towards moving the parsing of unstructured configuration path data
closer towards were configuration occurs, have the utility accept only
structured input for normalizing paths.
`Application.parse_preliminary_options_and_args` was previously, against
expectations, treating empty lists passed as the `argv` argument the
same way it treated `None`s.
This has been addressed and the correct behavior tested for in a unit
test of the `Application` class.
See issue #518 for details.
~40% improvement over status quo (perf measurements are best-of-5)
### before
```console
$ time flake8 /dev/null
real 0m0.337s
user 0m0.212s
sys 0m0.028s
```
### after
```console
$ time flake8 /dev/null
real 0m0.197s
user 0m0.182s
sys 0m0.012s
```
